Non-Enzymatically Colorimetric Bilirubin Sensing Based on the Catalytic Structure Disruption of Gold Nanocages

Red emitting fluorescence sensor based on Eu-tungstate complex for the detection of bilirubin in biological fluid

Bilirubin is an important biomarker indicative of human health metabolism, especially in jaundice disease. In this work, we develop an Eu (Europium)-tungstate complex-based turn-off luminescence detection method for bilirubin in human (urineand serum)samples. The Eu-tungstate complex was synthesized by a straightforward one-pot procedure at ambient temperature, utilizing Europium chloride and Sodium tungstate as the precursors. The Eu-tungstate complex exhibited a very strong red emission and demonstrated excellent stability. The fluorescence of the Eu-tungstate complex in aqueous mediacan be turned off regularly by the gradual addition of bilirubin with a limit of detection (LoD) of 0.27 μM and alimit of quantitative (LoQ) of 0.91 μM.Moreover, this sensing technology can be utilized to sense bilirubin in actual samples.

Cu-MOFs@AuPtNPs nanozyme-based immunosorbent assay for colorimetric detection of alpha-fetoprotein

Accurate detection of tumor biomarkers in blood is crucial for diagnosing and treating tumor disease. In this study, a metal enzyme-linked immunosorbent assay (MeLISA) was fabricated for the ultrasensitive and naked-eye detection of tumor biomarker alpha-fetoprotein (AFP) in clinical serum samples. Herein, novel copper metal-organic frameworks and gold platinum nanoparticle composites (Cu-MOFs@AuPtNPs) were synthesized for the first time by an in situ method, which showed an enormous specific surface area and excellent peroxidase (POx) mimicking properties. Cu-MOFs@AuPtNPs linked with antibodies targeting AFP served as a signal nanoprobe to amplify the detection signal. Additionally, the specificity of MeLISA was significantly enhanced through a conventional antigen-antibody reaction and efficient blocking of non-specific sites with BSA. Under optimal conditions, the sandwich-type MeLISA exhibited a wide range from 0.001 to 1000 ng mL-1 (R2 = 0.997) and a low detection limit of 0.86 pg mL-1 (S/N = 3) with acceptable stability, selectivity, and reproducibility. It is noteworthy that the suggested MeLISA performed exceptionally well in detecting clinical serum samples, which were visible to the naked eye and did not require complex platforms. To sum up, the innovative MeLISA based on Cu-MOFs@AuPtNPs provides an alternative method for early cancer diagnosis, particularly in economically backward areas where simple diagnostic apparatus is extremely desirable.

Fluorescent Nitrogen-doped Carbon Dots-based Turn-off Sensor for Bilirubin

Bilirubin (BR), a heme protein produced from breakdown of haemoglobin is present in aged red blood cells; whose abnormal concentration is associated with diseases like hyperbilirubinemia, coronary disease, iron deficiency, and so on. Herein, we have synthesized a selective, sensitive, and low-cost sensing platform using fluorescent nitrogen doped carbon dots (NCDs), prepared from precursors; citric acid and urea via a simple microwave-assisted method. The emission at 444 nm on excitation with 360 nm was well quenched in presence of BR suggesting a direct turn-off detection for BR. Characterization of developed probe was done by UV-Visible absorption studies, photoluminescence studies, SEM, TEM, ATR-FTIR, XPS, and DLS analysis. BR was detected with a Limit of Detection (LoD) and Limit of Quantification (LoQ) of 0.32 µM and 1.08 µM respectively. NCDs exhibited excellent selectivity and sensitivity towards BR in the presence of co-existing biomolecules and ions. Practical feasibility was checked by paper-strip-based sensing of BR and spiked real human samples were used for conducting real sample analysis.

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.

Fluorescence-Based Portable Assays for Detection of Biological and Chemical Analytes

Fluorescence-based detection techniques are part of an ever-expanding field and are widely used in biomedical and environmental research as a biosensing tool. These techniques have high sensitivity, selectivity, and a short response time, making them a valuable tool for developing bio-chemical assays. The endpoint of these assays is defined by changes in fluorescence signal, in terms of its intensity, lifetime, and/or shift in spectrum, which is monitored using readout devices such as microscopes, fluorometers, and cytometers. However, these devices are often bulky, expensive, and require supervision to operate, which makes them inaccessible in resource-limited settings. To address these issues, significant effort has been directed towards integrating fluorescence-based assays into miniature platforms based on papers, hydrogels, and microfluidic devices, and to couple these assays with portable readout devices like smartphones and wearable optical sensors, thereby enabling point-of-care detection of bio-chemical analytes. This review highlights some of the recently developed portable fluorescence-based assays by discussing the design of fluorescent sensor molecules, their sensing strategy, and the fabrication of point-of-care devices.